This project is studying 1) the nature of the Z-disk in striated muscle; 2) the properties and physiological role of purified alpha- actinin, a Z-disk protein; 3) purification and properties of M-line proteins, and 4) the assembly of myosin and actin into myofibrils. Z- disks are being studied by using polyacrylamide gel electrophoresis of Z-disk-containing preparations dissolved in urea or in sodium dodecyl sulfate to learn the number of different proteins that constitute the Z- disk. The physiological role of alpha-actinin is being studied by attempting to learn whether alpha-actinin has any effect of F-actin structure, and also by using antibodies to highly purified alpha-actinin to determine whether alpha-actinin exists in movement systems other than striated muscle. Binding of alpha-actinin antibodies in movement systems such as brush borders of intestinal cells or fibroblasts will not only indicate that alpha-actinin exists in these systems but will also indicate the location of alpha-actinin in these systems. M-line proteins will be purified; the purification procedure will be monitored by using antibody production to detect those fractions that elicit antibodies that bind to the M-line region. The effect of purified M- line proteins on aggregation of purified myosin to form filaments will be studied. The assembly of myofibrils will be studied by using cells grown in tissue culture and antibodies to purified alpha-actinin and M- line proteins to learn the point in differentiation of muscle cells that alpha-actinin and M-line proteins first appear. Appearance of these proteins before assembly of myofibrils may indicate that Z-disk and M- line proteins are necessary for proper three-dimensional assembly of actin and myosin filaments.